Pump components, such as pump pistons that move while pumping the fluid to be delivered, or stationary components sealing these, such as sealing rings, are usually subject to higher wear. The wear concerns surface regions that are subjected to pressure or contact pressure on a regular basis. Pump pistons, for instance, have relatively high wear due to oscillations, lateral forces and friction; in addition fission extrusion at the sealing ring, wear at the guide ring or at the eccentric shaft may occur on a regular basis. For example, the rotational movement of the drive is converted into a lifting movement for pressure generation via the bearing between the eccentric shaft and pump piston, which produces wear loads in the bearing.
Not only pump pistons but sealing rings as well must therefore be protected from increased wear so as to maintain their pumping and sealing function.
The described pump pistons and sealing rings are used, for example, in pump systems of modern automotive technology. Safety technologies such as ABS (anti-lock braking system), ESP (Electronic Stability Program), EHB (Electro-Hydraulic Braking) or TCS (Traction-Control Systems) are mentioned in this context by way of example.
In addition to uncoated pump pistons and sealing rings, lubricant-coated sealing rings are currently utilized as well, sometimes with additional lubrication in order to ensure the highest possible wear resistance.
In conventionally installed components in pumps, in particular for the afore-mentioned applications, the wear is sufficiently low for the normal service life of approximately 80 hours. Due to multiple application uses, for example in Enhanced-ESP or EHB, an increase to approximately 150 to 400 hours is expected in the required service life. When using the current sealing systems, the increase in the load duration may result in leaking brake fluid and thus a breakdown of the overall system due to wear of the sealing rings or pump pistons.
A typical material for sealing rings made of elastomeric materials, for instance, is EPDM (terpolymers of ethylene, propylene and a diene having an unsaturated part of the diene in the side chain).
The current measures for surface coating of sealing rings of elastomeric materials with a lacquer layer, such as spray or immersion coating, are of insufficient or only limited benefit in meeting the mentioned higher demands.
European Patent No. 0 022 285, describes a dry-film lubricated friction bearing in which a sliding layer between the surfaces of the bearing that move towards or against each other is made of a carbon layer applied on a substrate in a firmly bonding manner, which has a layer thickness in the range of 10 nm to 10 μm of a diamond-like crystal structure. However, these sliding layers can only be utilized with still acceptable wear under dry conditions, for instance without lubricants or in moisture-free ambient air, which is disadvantageous in practice.